Microelectronic substrates are exposed to a variety of physical, thermal, and chemical processes during the manufacture of a microelectronic device. For example, sputter deposition tools can deposit films on a substrate, high-temperature furnaces can grow films on the substrate, and chemical etching equipment can pattern films. All of these processes can leave a variety of residues and particles on the surface of a substrate, which, if not removed, can contaminate the substrate surface and deleteriously impact the performance of a microelectronic device. For example, conductive contaminates at the substrate surface can electrically short together two or more regions of an electrical element (e.g., a transistor, resistor, or capacitor) such that the electrical element does not function properly. In fact, the failure of this one element can in turn affect other electrical elements and ultimately disable or corrupt the entire microelectronic device. To mitigate effects such as these, microelectronic manufacturing processes implement a variety of cleaning processes that can remove surface contaminants.
One cleaning process in particular uses sonic pressure waves to remove particles from a substrate surface. This cleaning process typically involves submerging a substrate in a liquid and using the pressure waves to induce cavitation events proximate the substrate surface. These events can impart cavitation energy to particles attached to the surface that can remove or detach the particles. Depending on the type of sonic frequencies employed, this type of process can be referred to as an ultrasonic clean (having frequencies greater than 20 KHz but generally less than 800 KHz) or a megasonic clean (having frequencies of about 800 KHz or greater).
In general, megasonic cleaning processes typically impart less cavitation energy than ultrasonic cleaning processes. Consequently, ultrasonic cleaning processes typically remove more particles than megasonic cleaning processes, but ultrasonic cleaning processes typically induce more damage to the features of a substrate (e.g., patterned oxide, polysilicon, and metal). As microelectronic devices are manufactured to be smaller and more compact, they include smaller and more delicate features. Accordingly, the substrates that carry these devices are more likely to be cleaned with a megasonic cleaning process. Unfortunately, however, the lower cavitation energies of megasonic cleaning processes may not sufficiently remove surface particles.